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Astronomy
Earth, Moon, and Sky
| Details |
|---|
| The Sun is about 400 times larger than the Moon. By coincidence, it is also about 400 times farther away. |
| The Sun's apparent path through our sky is along the ecliptic, and the moon's path is almost along the ecliptic. Each month, there are two nodes where the moon crosses the ecliptic plane. The nodes shift slowly over eighteen years. |
| There are two types of eclipses, and both need the moon to be at a node of its orbit. We call that time frame eclipse season. |
| Moon's orbit is not circular. Sometimes it is closer (and bigger). Sometimes it is farther (and smaller). It isn't changing actual size it is changing angular size. |
| Perigee: Supermoon appears fourteen percent bigger and thirty percent brighter than micromoon. |
| Apogee: micromoon |
| Because the ratio of physical sizes is similar to the ratio of their distances, the moon and the sun have a very similar angular size on our sky (0.5 degrees). This is a pure coincidence, and it means the moon is often able to completely cover the Sun. |
| Penultimate: second to last |
| If illuminated by a light source, any object can cast a shadow. There will be a zone of partial shadow, the penumbra, and a zone of full shadow, the umbra. |
| On August 21st, 2017, there was a total solar eclipse, visible from Oregon to South Carolina. |
| At the point of totality, the Sun's corona becomes visible! In Gallatin, totality for the 2017 eclipse was only 160 seconds. |
| On April 8th, 2024 there will be another "Great American" Total Solar Eclipse that does not require a flight around the world to watch. |
| If you are close to the path of a total solar eclipse but not quite lined up, just like Grand Rapids was in August 2017, then you might observe a partial solar eclipse. |
| If the Moon cannot fully block the Sun, there can be an annular solar eclipse. This composite image is from May 20, 2012 in Red Bluff, California. We get this kind of eclipse if the Moon is near the farthest point in its orbit when also at a node. |
| There are total, annular, and partial solar eclipses. |
| Required Conditions: must be an eclipse season (nodes in right spot); observer must be in the narrow path of totality (or annularity), or near enough to see a partial eclipse; the moon must be in the New Moon phase. |
| There are three types of lunar eclipses: Penumbral eclipses; partial lunar eclipses; total lunar eclipses. |
| The shape of the Moon during the hours of a Lunar Eclipse does not match the phase shapes. |
| Because the Earth's shadow provides a large target, total lunar eclipses are slightly more common than total solar eclipses, since there is no chance the shadow is too small (as it is in annular solar eclipses). |
| Conditions for a Lunar Eclipse: must be an eclipse (nodes); observer must be on night/evening side of Earth when the alignment occurs; the Moon must be in the Full Moon phase. |
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